1. Field of the Invention
The present invention generally relates to a communication system capable of system having an improving a data transmission efficiency of a Transmission Control Protocol (TCP) in a wireless network environment and a method thereof.
2. Description of Related Art
FIG. 1 is a view illustrating an example of data transmission and reception of a transmitting end 10 and a receiving end 20 according to the TCP of the conventional communication system. Referring to FIG. 1, to heighten the reliability of data transmission and reception, the TCP uses a method of transmitting an acknowledgement (ACK) packet so that the receiving end 20 acknowledges the data reception to the transmitting end 10. If the ACK packet is not received after a specified time elapses, the transmitting end 10 determines that the packet is lost during the transmission, and retransmits the packet.
In the existing wire network environment, most packet losses occur due to network congestion. If the packet loss occurs due to the network congestion, the TCP drives a congestion control mechanism for controlling the amount of data transmission. The TCP congestion control mechanism may be a slow start mechanism, a congestion avoidance mechanism, or a fast retransmit and recovery mechanism, and the amount of data transmission is adjusted according to the state of network through this mechanism.
In a wireless network, being different from the wire network, most packet losses occur due to the characteristic of a wireless link, that is, high error rate and handoff, rather than the network congestion. Accordingly, the control mechanism of the TCP proposed to match the characteristic of the wire network environment cannot properly cope with a mobile network environment. Specifically, since the packet loss wirelessly occurring due to a packet error is processed in the same manner as that occurring due to the network congestion, the slow start or fast recovery mechanism reduces a congestion window size in the same manner as the packet loss occurring due to the congestion. In other words, if the TCP of the wire network is applied to the wireless network, because all the packet losses occur due to the network congestion, the TCP unnecessarily lowers the transmission speed. As a result, due to the repeated packet losses, the bandwidth of the link is wasted, and this deteriorates the performance of the whole network.
For the above-described reason, it is recognized as an important matter to efficiently use the TCP in the wireless network. That is, it is important to improve the TCP, which has been developed to be suitable to the wire network, to match the characteristic of the wireless network and to properly cope with the packet loss due to the packet error rather than due to the congestion.
Techniques for solving TCP performance deterioration in the wireless network environment may be divided into a split connection method, a proxy-based method, and an end-to-end method. A representative split connection method may be an Indirect-TCP (I-TCP) method. The I-TCP method controls the TCP by dividing one TCP connection into two connections, that is, one connection between a source node and a wireless router and the other connection between the wireless router and a moving node, in order to conceal the packet loss on the wireless link from the source node.
A representative proxy-based method may be a snoop method. The snoop method controls the wireless router to retransmit the packet when the packet loss occurs on the wireless link. The Internet Engineering Task Force (IETF), which is an Internet standardization group, recommends the snoop method. However, this method has the drawbacks in that it cannot improve the performance deterioration of the TCP when a long disconnection occurs on the wireless link. Specifically, when the packet loss occurs on the wireless link, the source node does not retransmit the packet, but the wireless router locally retransmits the packet. If a degradation between a specified terminal and the wireless link is maintained during the retransmission of the packet, packet transmission to other terminals is not performed due to the repeated attempts to retransmit the packet to the specified terminal, and thus the performance deterioration of the TCP is not improved.
A representative end-to-end method may be a Freeze-TCP (F-TCP) method. The F-TCP method solves the problems of performance deterioration by informing the source node that the source node maintains its state before the occurrence of the error when the packet loss occurs on the wireless link. The F-TCP method focuses on the solving of the problems of performance deterioration during a handoff.